In recent years, knee air bag devices for vehicles, that expand and unfold a knee air bag at the time of a collision and restrain the knees of a vehicle occupant, are being installed from the standpoint of improving the vehicle occupant protecting performance at the time of a collision. Examples of this type of knee air bag device for a vehicle are disclosed in following Patent Documents 1, 2. To describe briefly, in the prior art disclosed in these Patent Documents, a knee air bag device is incorporated within the glove compartment door of a glove compartment that is provided at an instrument panel.    Patent Document 1: German Patent No. 4209604    Patent Document 2: U.S. Pat. No. 6,276,713